Metering equipment is the primary means by which an electric utility company periodically measures the amount of electrical energy or power used by each of its customers. One type of metering equipment that is commonly used for domestic or home metering is the "watt-hour meter." The watt-hour meter is essentially an electric motor that runs in proportion to the power being used by the customer and which records the energy used by the customer over the billing period. For larger customers, the utility company charges for low power factors and the metering equipment may also include a reactoformer along with the watt-hour meter to record the reactive volt-ampere-hours during a billing period. Similarly, the utility company will generally charge for "demand" and the metering equipment may include a reactive demand meter which records reactive demand.
In that currently available metering equipment generally employ electro-mechanical measuring devices, they must be periodically tested to ensure that they are accurately measuring the energy consumed by the customer. Presently, some utility companies perform a simple field test on the meters to determine whether they are working properly. If the meter is not working correctly, the technician will bring the defective meter to a central testing location where the meter will be recalibrated for later use. In view of the large number of meters in service, however, a growing number of utility companies prefer to test and if necessary, recalibrate the meter directly in the field. This combined field testing and on-site recalibration process saves a great deal of time and money.
U.S. Pat. No. 4,646,003 discloses an apparatus for testing a watt-hour meter at the operational site of the customer. Apparatus of this type generally apply a phantom load to the meter and to a watt transducer. The watt-hour reading of the meter is compared to an ideal watt-hour figure computed by the watt transducer based upon the actual test currents, and the result of that comparison is represented as a percentage error. The watt-hour readings of such meters are commonly determined by a light sensing device which senses each rotation of the disc within the meter and then outputs a signal indicative of the number of rotations to the watt transducer.
Apparatus of this type, however, have several disadvantages. In particular, such apparatus require the technician to test the meter at the customer's meter box which is normally located outdoors. Because such test apparatus employ a light sensor to count the disc rotations, rainy or snowy weather conditions may make such measurements difficult and inaccurate. Furthermore, cold and unpleasant weather conditions may create such an uncomfortable working environment that the technician may be inclined to rush the testing process whereby the accuracy may be adversely affected. Additionally, such apparatus are heavy and cumbersome to carry to the customer's meter box which sometimes may be located quite a distance from the street and/or positioned in awkward places.